Imaging of acute pulmonary embolism

Acute pulmonary thromboembolism (PE) is a cardiovascular emergency associated with significant morbidity and a 5-35 % mortality for untreated pulmonary embolism. If promptly diagnosed and treated, the mortality rate can be significantly reduced. Diagnosis of acute PE continues to be a clinical challenge, with diagnostic imaging playing an important role. This review discusses the clinical challenges of diagnosing acute PE, presents an evidence-based review of the current tests and ever-evolving imaging technology, and highlights special considerations related to radiation dose, contrast media use, and pregnant patients.

Cardiovascular disasters in pregnancy

Cardiovascular emergencies in pregnancy are rare but often catastrophic. This article reviews the diagnosis and management of venous thromboembolism, aortic dissection, acquired heart disease and cardiomyopathy, acute myocardial infarction, and cardiac dysrhythmias in the setting of pregnancy. It also reviews updated resuscitation guidelines for cardiac arrest and perimortem cesarean section.

Venous thromboembolism associated with pregnancy and hormonal therapy

Venous thromboembolism (VTE) is a major cause of maternal morbidity and mortality during or early after pregnancy and in women taking hormonal therapy for contraception or for replacement therapy. Post-thrombotic syndrome, including leg oedema and leg pain, is an unrecognized burden after pregnancy-related VTE, which will affect more than two of five women. Women with a prior VTE, a family history of VTE, certain clinical risk factors and thrombophilia are at considerably increased risk both for pregnancy-related VTE and for VTE on hormonal therapy. This review critically assesses the epidemiology and risk factors for pregnancy-related VTE and current guidelines for prophylaxis and treatment. We also provide information on the risk of VTE related to hormonal contraception and replacement therapy.

Imaging of pregnant and lactating patients: part 2, evidence-based review and recommendations

OBJECTIVE

The objectives of this article are to discuss the current evidence-based recommendations regarding the use of diagnostic imaging in the evaluation of pulmonary embolism, appendicitis, urolithiasis, and cholelithiasis during pregnancy.

CONCLUSION

Diagnostic imaging should be performed during pregnancy only with an understanding of the maternal and fetal risks and benefits, the comparative advantages of different modalities, and the unique anatomic and physiologic issues associated with pregnancy.

Pulmonary embolism

Pulmonary embolism (PE) remains one of the most challenging medical diseases in the emergency department. PE is a potentially life threatening diagnosis that is seen in patients with chest pain and/or dyspnea but can span the clinical spectrum of medical presentations. In addition, it does not have any particular clinical feature, laboratory test, or diagnostic modality that can independently and confidently exclude its possibility. This article offers a review of PE in the emergency department. It emphasizes the appropriate determination of pretest probability, the approach to diagnosis and management, and special considerations related to pregnancy and radiation exposure.

American Thoracic Society documents: an official American Thoracic Society/Society of Thoracic Radiology Clinical Practice Guideline--Evaluation of Suspected Pulmonary Embolism in Pregnancy

BACKGROUND

Pulmonary embolism (PE) is a leading cause of maternal mortality in the developed world. Along with appropriate prophylaxis and therapy, prevention of death from PE in pregnancy requires a high index of clinical suspicion followed by a timely and accurate diagnostic approach.

METHODS

To provide guidance on this important health issue, a multidisciplinary panel of major medical stakeholders was convened to develop evidence-based guidelines for evaluation of suspected pulmonary embolism in pregnancy using the Grades of Recommendation, Assessment, Development, and Evaluation (GRADE) system. In formulation of the recommended diagnostic algorithm, the important outcomes were defined to be diagnostic accuracy and diagnostic yield; the panel placed a high value on minimizing cumulative radiation dose when determining the recommended sequence of tests.

RESULTS

Overall, the quality of the underlying evidence for all recommendations was rated as very low or low with some of the evidence considered for recommendations extrapolated from studies of the general population. Despite the low quality evidence, strong recommendations were made for three specific scenarios: performance of chest radiography (CXR) as the first radiation-associated procedure; use of lung scintigraphy as the preferred test in the setting of a normal CXR; and performance of computed-tomographic pulmonary angiography (CTPA) rather than digital subtraction angiography (DSA) in a pregnant woman with a nondiagnostic ventilation-perfusion (V/Q) result.

DISCUSSION

The recommendations presented in this guideline are based upon the currently available evidence; availability of new clinical research data and development and dissemination of new technologies will necessitate a revision and update.

Pulmonary CT angiography protocol adapted to the hemodynamic effects of pregnancy

OBJECTIVE

The purpose of this study was to compare the image quality of a standard pulmonary CT angiography (CTA) protocol with a pulmonary CTA protocol optimized for use in pregnant patients with suspected pulmonary embolism (PE).

MATERIALS AND METHODS

Forty-five consecutive pregnant patients with suspected PE were retrospectively included in the study: 25 patients (group A) underwent standard-protocol pulmonary CTA and 20 patients (group B) were imaged using a protocol modified for pregnancy. The modified protocol used a shallow inspiration breath-hold and a high concentration, high rate of injection, and high volume of contrast material. Objective image quality and subjective image quality were evaluated by measuring pulmonary arterial enhancement, determining whether there was transient interruption of the contrast bolus by unopacified blood from the inferior vena cava (IVC), and assessing diagnostic adequacy.

RESULTS

Objective and subjective image quality were significantly better for group B-that is, for the group who underwent the CTA protocol optimized for pregnancy. Mean pulmonary arterial enhancement and the percentage of studies characterized as adequate for diagnosis were higher in group B than in group A: 321 ± 148 HU (SD) versus 178 ± 67 HU (p = 0.0001) and 90% versus 64% (p = 0.05), respectively. Transient interruption of contrast material by unopacified blood from the IVC was observed more frequently in group A (39%) than in group B (10%) (p = 0.05).

CONCLUSION

A pulmonary CTA protocol optimized for pregnancy significantly improved image quality by increasing pulmonary arterial opacification, improving diagnostic adequacy, and decreasing transient interruption of the contrast bolus by unopacified blood from the IVC.

Influence of population prevalences on numbers of false positives: an overlooked entity

BACKGROUND

Disease prevalence alters the number of true positives (TP), true negatives (TN), false negatives (FN), and false positives (FP), even if the sensitivity and specificity of a test stays the same.

METHODS AND MATERIALS

We illustrate this using data for the detection of suspected acute pulmonary embolism (PE) from the Prospective Investigation of Pulmonary Embolism Diagnosis II (PIOPED II). We chose PE because of the clinical significance of the disease, the low prevalence of PE in the patient population being tested with CTPA with the widespread adoption of CTPA, and the serious clinical consequences of anticoagulation therapy in FP patients.

RESULTS

Based on PIOPED II data (sensitivity 83%, specificity 96%), at a disease prevalence of approximately 5%, the number of FP patients is greater than the number of TP patients. Scaled to the US population, at a disease prevalence of 5%, there would be 139,800 FPs and 3,356,200 TNs. Assuming a mortality rate of 0.5% and a 3.0% rate of major bleeding secondary to anticoagulation therapy for well-controlled patients, if all FP patients received anticoagulation, there would be 699 deaths and 4194 major bleeding complications.

CONCLUSIONS

At a prevalence of approximately 5% for PE, the number of FPs approaches or is greater than the number of TPs for CTPA for the detection of suspected acute PE. Patients with FP results may receive unnecessary, potentially harmful treatment with anticoagulation therapy. Population prevalence of disease needs to be taken into account along with the diagnostic accuracy of a test, because this may significantly affect downstream patient outcomes.

The diagnostic management of acute venous thromboembolism during pregnancy: recent advancements and unresolved issues

Adequate diagnostic management of suspected venous thromboembolism (VTE) in pregnant women is of great importance. The diagnostic performance of clinical decision rules and D-dimer testing is influenced by physiological changes during pregnancy and is understudied. Recent studies have addressed these issues by developing a new clinical decision rule and raising the D-dimer level cut-off points. With imaging of suspected pulmonary embolism (PE) the radiation exposure remains a concern. Recent studies have adjusted CT settings and scan length to minimize this exposure without loss of image quality. Furthermore the first choice imaging modality of suspected PE in pregnant women remains a matter of debate in view of studies showing high inadequacy rates for both CT scanning and VQ scanning. Issues concerning the diagnostic management of VTE in pregnant women and advancements made in recent years will be discussed.

Challenges, controversies, and hot topics in pulmonary embolism imaging

OBJECTIVE

The purpose of this article is to discuss the diagnostic role of pulmonary CT angiography (CTA) in the workup of pulmonary embolism (PE), including specific populations, and issues such as pulmonary CTA combined with indirect CT venography; radiation dose considerations; the management of isolated subsegmental PE; and new technologic developments, such as dual-source/dual-energy pulmonary CTA.

CONCLUSION

The role of pulmonary CTA will continue to grow with the emergence of MDCT and dual-energy CT and their improved capabilities. However, the need for any given CT examination should always be justified on the basis of the individual patient's benefits and risks.